My ranger heater is acting wierd. The air blows out defrost no matter what I have it set on. Although It will switch to vent or whatever I set it to when I am not forcing the engine or at idle but when I am forcing the engine whether to climb a hill or to pickup speed, the heat will switch back to the defrost till I stop forcing the engine then it will go back to the vent. Anyone know what my problem could be?

 

Somewhere in the system you have a vacuum leak. There is a vacuum cannister under the hood and a line going inside the truck. Check for a vacuum leak on all the lines and actuators and on back of the switch.